Heat treatment of steel rails



Patented Oct. 3, 1933- PATENT OFFICE 1,929,346 HEAT TREATMENT OF STEEL RAILS John Brunner, Chicago, 111.

No Drawing. Original application October 22,

1931, Serial No. 570,496. Divided and this appiication June 11, 1932. Serial No. 616,760

6 Claims.

This invention relates to metallurgy and more particularly to the heat treatment of metals and alloys to improve the qualities thereof and still more particularly to the heat treatment of steel rails. This application is a divisional application of application Serial No. 570,496 filed October 22, 1931 entitled Heat treatment of steel rails.

This invention is substantially an improvement of the invention set forth in my U. S. Patent No.

1,277,372 issued September 3, 1918.

. The process of U. S. Patent No. 1,277,372 substantially comprises a method of heat treating steel rails to obtain therein a more uniform and fine grain structure and a better surface than had heretofore been obtainable. The method substantially comprises rolling the rail to a section larger than the desired finished section; cooling the rail to temperatures below the thermal critical range; reheating the rail to temperatures above the thermal critical temperatures (approximately 800 0.); rolling the rail to the desired finished section; and slowly cooling the rail to room temperatures; This method produced a finished rail having a fine grain structure which imparted thereto great toughness. The rail product, however, did not possess sufficient surface hardness to make it resistant to severe service conditions.

One of the objects of the present invention is to increase the surface hardness of the rail product of my prior invention.

Another object of the present invention is to provide heat-treating methods whereby the surface hardness of a steel rail may be materially increased at its ends where the greatest abrasion and battering takes place in service under the rolling loads of motive power and transportation equipment. 7

Another object of the present invention is to provide a steel rail having an interior of relatively high ductility throughout the entire length of the rail and an exterior of relatively high hardness at the ends of the rail.

Another object of the present invention is to improve and facilitate the manufacture of steel rails.

Other objects and advantages will be apparent as the invention is more fully disclosed.

In accordance with the objects of the present invention 1 have found that I may impart a relatively high surface hardness to the relatively tough fine grain structure in the rail prepared in accordance with the invention of my prior patent. thereby materially increasing the resistance of the rail to service conditions, by subjecting the rail to certain heat-treating methods. The heattreating methods substantially comprise the following steps:

At the conclusion of the final rolling operation the finished rail is cooled to temperatures approximating 300 C., and is then reheated to rel- 5 atively uniform temperatures which are slightly above the thermocritical range of the specific composition of steel used therein and then cooling the head of the rail at and near its ends in a quenching medium until the surface temperature of this part of the rail has been lowered at least partially through the blue-heat range (approximately 288 to 316 C.) but to temperatures not lower than 200 C.; thereafter the rail is reheated to relatively uniform temperature. above about 0 300 C. but below the thermal critical range for a determined time interval and is then allowed to slowly cool to atmospheric temperatures. 0

In this manner I first effect a refinement of the internal grain structure of the rail, increasing its uniformity and toughness, and then a hardening of the surface of the head thereof at and near its ends, thereby obtaining a desired amount of external surfacehardness of the rail ends to resist abrasion and battering of the rail ends in the track in service, and a subsequent annealing or tempering to remove internal stresses and strains incident to the hardening operation.

As a specific embodiment of the practice of this invention I will disclose the method as applied to steel rail composition comprising carbon .40 to .85%; manganese .40 to 1.60%; phosphorus, not over 08%; sulphur, not over 08%; silicon, not

over 1.50%, depending on the section of rail used and the intended service of the treated rail.

In accordance with the teaching of my prior patent a billet of steel in the above noted composition is heated to temperatures above the thermal critical range and rolled into a section approximating but larger than the desired finished rail section and then is cooled to temperatures below the thermal critical range. Preferably but not necessarily the per cent reduction in area remaining is only that which is sufilcient to obwe tain an accurate section of the rail.

The cooled rail is then reheated to relatively uniform temperatures approximating 800 C. and is thereafter rolled to the desired finished section. The finished rail is thereafter allowed to cool to 1 an average temperature of not less than 300 C. and is again reheated to relativelyuniform temperatures approximating 800 0., and from these temperatures is quenched on the head at and near both ends of the rail until the surface tempera- 119 tures of this part of the rail has been lowered partially through the blue-heat range but not lower than 200 C. After the quenching of the ends the rail is placed into a furnace and heated to relatively uniform temperatures above 300 C. but below the thermal critical range (600 C.) for a predetermined time interval approximating from one-half to two hours, following which it is allowed to cool slowly'in the air to atmospheric temperatures. The exact cooling temperatures and the time intervals of cooling may be widely varied, depending upon the composition of the steel, the degree of surface hardness desired, and upon the internal structure desired in the rail.

The rail product thus produced will be found to have retained the fine grain structure of my prior patent with an exterior surface on top of the head at the end of the rail of greater hardness than heretofore obtainable by cold working means alone. For example, the finished rail product of my prior patent will have a surface hardness of approximately 250-280, as measured on the Brinell scale. The finished rail product of the specific embodiment of the present invention will have a surface hardness of the head at and near the ends of the rail approximating from 340 to 410, depending on the section and intended service of the heat treated rail.

The exact cooling temperatures and the time intervalsof cooling may be widely varied depending upon the composition of the steel, the finished hardness desired, and upon the internal grain structure desired in the rail.

While I have disclosed as a specific embodiment the steps of rolling the rail to a section larger than the desired finished section, cooling to below and then reheating to above the thermal critical range, and then rolling to the desired finished section, I may omit this particular sequence of steps and roll the rail directly down to the desired finished section if desired. The

rail thus prepared may be cooled to temperatures below the thermal critical range, but above 300 C., reheated to temperatures approximating but above the thermal critical range, and there-- I comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling to a section larger than the desired finished rail section, cooling to temperatures below the thermal critical range, but above about 300 C., reheating to temperatures approximating but above the thermal critical range, rolling to the desired finished section. cooling to temperatures below the thermal critical range but above 300 C., reheating to temperatures apbut above the thermal critical range, quenchingthe head of the rail at and near its ends until the surface temperatures of the head at and near its ends lie within the blue-heat range but above about 200' C., reheating to temperatures above 300 C., but below the thermal critical range and thereafter cooling slowly to room temperatures.

2. The method of forming steel rails having an approximate composition of carbon .40 to .85%; manganese .40 to 1.60%; Phosphorus, not over .08%; sulphur, not over .08%; silicon, not over 1.50%; which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling to a section larger than the desired finished section, cooling to temperatures lower than the thermal critical range, but above about300" C., reheating to temperatures approximating but above the thermal critical range, rolling to the desired finished section, cooling to temperatures below the thermal critical range, but above about 300 C., reheating to temperatures approximating but above the thermal critical range, quenching the head of the rail at and near its ends until the surface temperatures of the head at and near its ends lie within the blue-heat range but above 200 C., annealing the rail at temperatures approximating 600 C., and thereafter slowly cooling to atmospheric temperatures.

3. The method of forming steel rails having an approximate composition of carbon .40 to .85%; manganese .40 to 1.60%; phosphorus, not over .08%; sulphur, not over .08%; silicon, not over 1.50%; which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling to a sectionlarger than the desired finished section, cooling to temperatures lower than the thermal critical range, but above about 300 C., reheating to temperatures approximating but above the thermal critical range, rolling to the desired finished section, cooling to temperatures below the thermal critical range, but above about 300 C., reheating to temperatures approximating but above the thermal critical range, quenching the head ofthe rail at and near its ends until the surface temperatures of the head at and near its ends lie within the blue-heat range but above 200 C.,

hours, and thereafter slowly cooling to strum"- pheric temperatures.

4. The method of forming steel rails which comprises heating a rail ingot or billet to rolling temperatures above the thermal critical range, rolling the rail to the desired finished section, cooling the rail to temperatures below the thermal critical range but above about 300-C., reheating the rail to temperatures approximating but above the thermal critical range, quenching the headof the rail at and near its ends until the surface temperatures of the head at and near its ends approximate but are above 200 C., annealing to temperatures above about 300 C. but

below the thermal critical range and thereafter cooling slowly to room temperatures.

5. The method of forming steel rails from a rail ingot or billet having a composition of carbon .40 to manganese .40 to 1.60%; phosphorus, not over .08%; sulphur, not over, .08%; silicon, not over 1.50%; which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling the rail to the desired finished section, cooling the rail to temperatures below the thermal critical range but above about 300 C., reheating to temperatures approximating but above the thermal criticalrange,quenchingthehead oftherailatand near its ends imtil the surface temperatures of the head at and near its endsapproximate but areabove 200C.,annealingthe railtotemperu' hu'esabovemC.,butlessthantbethermal annealing the rail at temperatures approximat-;-- ing 600 C. for approxima' tely one-half to I critical range and thereafter slowly cooling to atmospheric temperatures.

6. The method of forming steel rails from a rail ingot or billet having a composition approximating carbon .40 to .85%; manganese, .40 to 1.60%; phosphorus, not over .08%; sulphur, not over 08%; silicon, not over 1.50%; which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling the rail to the desired finished section cooling the rail to temperatures below the ther- 

